I have a UPS that I have added extra batteries. The UPS came with one 12ah, I have added 2 18ah and a 35ah. The 12ah battery failed and pulled down the voltage to 11.75, the case was hot, when I disconnected the battery it read 4.5 volts. The batteries have been in this state for at least a month. Is there any chance that the three remaining batteries might still be good?
it is possible.
at 11.75v, all 6 cells in the (good) batteries are still above 1.75v.
so you probably haven't damaged them by overdischarge.
if the good batteries are located physically close to the damaged battery, they may have been heat damaged.
to find out for sure, i would do a reserve capacity test on the remaining good batteries.
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
Thanks, they should be fully charged in the morning. I will give the reserve capacity test a go.
2011 Nissan Leaf SL
If the batteries sat around discharged, that would be a bad thing. They may charge up, but have less capacity than before.
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